This invention relates to a printed circuit device including a printed circuit board and a heat plane associated with the board. In particular, the invention relates to a device of the type suitable for carrying electromagnetic compatibility (EMC) filters for removing, for example, high frequency noise currents from the power lines of the device. The invention also relates to a method of producing such a device.
In a known device, for example as described in GB 2320619, a printed circuit board carries circuits which are sensitive to electromagnetic radiation or which generate such radiation, and is provided with a series of openings through which connector elements extend. Each connector element is soldered, at one end, to appropriate tracks provided on or in the circuit board, the other end of each element being shaped for cooperation with a casing to electrically connect the said tracks to the casing. The board may be provided with a heat plane in the form of a copper or other suitable metallic plate which is bonded to a surface of the board and arranged to contact the casing. The heat plane is thus thermally and electrically connected to the casing. In such an arrangement, the heat plane is provided with a series of openings through which the connector elements extend. As a result, there is no direct electrical connection between the connector elements and the heat plane.
It is thought that, in use in applications in which significant levels of vibrations are applied to the device, the vibrations may result in the connector elements becoming abraded, resulting in failure of the device.
It is an object of the invention to provide a printed circuit device of relatively simple and convenient form in which this disadvantage is obviated or mitigated, and to provide a method of producing such a device.
According to the present invention there is provided a printed circuit device comprising a printed circuit board having an electrically conductive heat plane associated with a surface thereof, the circuit board having an opening formed therein which exposes a ground layer or track of the circuit board, a wall defining the opening being provided with an electrically conductive coating which is electrically connected to the ground layer or track, the heat plane being provided with a cut-out defining a projection which is bent to extend into the opening, the projection being secured to the coating to electrically connect the coating and the ground layer or track to the heat plane.
As the electrical connections to the ground layer or track are achieved through the parts of the heat plane which form the projections, and as the heat plane is of a relatively robust form, the risk of abrasion may be reduced.
The heat plane is conveniently provided with a plurality of such cut-outs defining a plurality of projections, each projection extending into a respective opening provided in the circuit board to form an electrical connection between the ground layer and the heat plane.
The or each projection is conveniently secured to the or a respective one of the coatings by soldering, for example using a wave soldering technique.
The heat plane conveniently takes the form of a metallic plate, for example a copper plate, an aluminum plate or a plate of steel, molybdenum or invar.
The invention also relates to a method of producing such a device comprising the steps of forming a cut-out in a heat plane, positioning the heat plane adjacent a printed circuit board such that a projection defined by the cut-out overlies a coated opening provided in the circuit board, the coating of the opening being electrically connected to a ground layer or track of the circuit board, deforming the heat plane to push the projection into the opening, and securing the projection to the coating of the opening to form an electrical connection between the ground layer or track of the circuit board and the heat plane.
According to another aspect of the invention there is provided a heat plane for use in such a device, the heat plane being provided with a cut-out defining a projection.